What are the implications of a very large scene (scale-wise, relative to the default cube)?
One important implication that's not immediately obvious is that Blender's light objects won't scale properly with the rest of the scene.  As the objects in your scene get bigger the lights will look dimmer and sharper.

Before scaling




After scaling




One way around this is to use the unit scale feature in the scene tab instead of scaling the objects manually.



Also note that unlike the blender lights, objects with emission materials have no issues scaling.